The present invention generally relates to data processing systems and more particularly to the organization of a so-called control store which is included in microprogrammed data processing systems.
In microprogrammed data processing systems, a control store having a plurality of locations is included whereby a substantial number of the operations as desired in the system are controlled by so-called firmware words included in each of such locations. Such microprogramming allows the system to be more flexibly operated, and avoiding committed logic to a large extent, by simply changing such firmware words thereby increasing the available computing power. The content of a firmware word is utilized to control a step in the data processing system's operation. The firmware words are linked together to provide a series of steps or instructions, i.e., a routine. Such linking is provided based upon various test conditions including the next address information of the current firmware word. The system requires that the control store be able to address itself based upon its own internal address information in each location and based on such test conditions. The address information contained in each such location of the firmware word are much more numerous than the number of opcodes which are included in the command field portion of each firmware word. Stated another way, each particular opcode may be grouped with different address codes. Thus, the opcodes are repeated much more often so as to be grouped with the various address codes which are required therewith under various conditions. For example, the various steps as represented by the opcodes may be arranged in different combinations to provide different firmware routines. Thus, the same opcode in different firmware words would include different next address information included therewith. Because of the redundancy of such opcodes, the storage locations in the control store are used to store the same information, thereby increasing cost and space required in the system.
It is accordingly a primary object of the present invention to provide a microprogrammed data processing system having an improved control store organization.